scholarly journals Numerical Models for Hydraulic Refracturing on Vertical Oil Wells

2018 ◽  
Vol 7 (4.26) ◽  
pp. 279 ◽  
Author(s):  
Vladimir Bratov
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Hydraulic Fracturing ◽  
Numerical Models ◽  
Fracture Initiation ◽  
Time Profile ◽  
Oil Wells ◽  
Fracture Event ◽  
History Of

The paper presents an approach for simulation of refracturing treatment on vertical oil wells. The model is accounting for filtration of hydraulic fracturing fluid through the proppant packed inside the crack formed during previous hydraulic fracturing treatments. The simulations provide a possibility to estimate history of stress intensity factor appearing at the tip of the existing crack once the time profile of pressure within the wellbore is given. Introducing critical value of the stress intensity factor for the fractured media, time-to-fracture initiation (after pressure increase start) can be estimated and compared to instance of fracture event registered in real conditions. Also, the possibility of fracture reorientation through formation of new fractures at the region adjacent to the wellbore is studied. 

Fracture Initiation Due to Asymmetric Impact Loading of an Edge Cracked Plate

1990 ◽  
Vol 57 (1) ◽  
pp. 104-111 ◽  
Author(s):  
Y. J. Lee ◽  
L. B. Freund
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Edge Crack ◽  
Crack Tip ◽  
Fracture Initiation ◽  
Stress Wave Propagation ◽  
Normal Velocity ◽  
Asymmetric Impact ◽  
Original Crack

The two-dimensional elastodynamic problem of a semi-infinite plate containing an edge crack is considered. Initially, the plate is stress-free and at rest. To simulate the asymmetric impact of a projectile on the cracked edge of the plate, a normal velocity is suddenly imposed on the boundary of the plate on one side of the edge crack. The boundary of the plate and the crack faces are otherwise traction-free. Due to the nature of the loading, a combination of transient mode I and mode II deformation fields is induced near the crack tip. The corresponding stress intensity factor histories are determined exactly by linear superposition of several more readily obtainable stress wave propagation solutions, including a fundamental solution arising from a particular problem in the dynamic theory of elastic dislocations. The stress intensity factor histories are determined for the time interval from initial loading until the first wave scattered at the crack tip is reflected at the plate edge and returns to the crack tip. In experiments on fracture initiation in a high-strength steel based on essentially this specimen and loading configuration, Kalthoff and Winkler (1987) reported a fracture grew from the original crack either as a tensile crack inclined to the original crack plane or as a straight-ahead shear fracture, depending on the intensity of the applied velocity. The observations are considered in light of the solution reported here.

The Extent of the Stress Intensity Factor Field During Crack Growth Under Dynamic Loading Conditions

1986 ◽  
Vol 53 (2) ◽  
pp. 303-310 ◽  
Author(s):  
C. C. Ma ◽  
L. B. Freund
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Singular Term ◽  
Dynamic Pressure ◽  
Fracture Initiation ◽  
Fracture Plane ◽  
Crack Face ◽  
Crack Faces

The phenomenon considered is fracture initiation and crack growth in a plate due to dynamic pressure loading on the faces of a pre-existing crack. The problem is formulated within the framework of two-dimensional elastodynamics, and the system is viewed as a semi-infinite crack in an otherwise unbounded body. At a certain instant of time, a spatially uniform pressure begins to act on the crack faces. The pressure magnitude increases linearly in time for a certain period (the rise time T), and it is constant thereafter. The crack begins to extend at constant speed at some time after the pressure begins to act (the delay time τ). The pressure acts only over the original crack faces, and both τ > T and τ < T are considered. The ratio of the normal stress on the fracture plane to the value due to the singular term in the stress field alone is computed for some point at a small fixed distance ahead of the crack tip, with a view toward establishing the conditions under which the stress intensity factor controlled singular term accurately describes the near tip stress distribution in this highly transient process. Measured and calculated histories compare very well for relatively low crack face pressures, but there is significant disagreement beyond crack growth initiation for higher pressures. Possible reasons for the discrepancies are discussed.

scholarly journals Numerical Analysis of Stress Intensity Factor in Specimens with Different Fillet Geometry Subjected to Bending

2018 ◽  
Vol 12 (1) ◽  
pp. 38-43
Author(s):  
Janusz Lewandowski ◽  
Dariusz Rozumek
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Numerical Analysis ◽  
Intensity Factor ◽  
Stress Ratio ◽  
Numerical Models ◽  
Stress Component ◽  
Numerical Calculations ◽  
Stress Intensity Factor Range ◽  
Cyclic Bending

AbstractThe article presents the maps of xx stress component and compares values of analytical and numerical calculations for the stress intensity factor range of welded specimens with fillet welds which subjected to cyclic bending. The tests were performed under constant value of moment amplitude Ma= 9.20 N·m and stress ratio R = σmin/ σmax= −1. The specimens were made of drag steel rod S355. The specimens were solid and welded. The numerical models were simulated with ABAQUS suite and numerical calculations performed with FRANC3D software.

Determination of Dynamic Fracture-Initiation Toughness Using a Novel Impact Bend Test Procedure

1993 ◽  
Vol 115 (4) ◽  
pp. 389-397 ◽  
Author(s):  
T. Yokoyama
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Dynamic Fracture ◽  
Dynamic Stress ◽  
Test Procedure ◽  
Dynamic Stress Intensity Factor ◽  
Fracture Initiation ◽  
Initiation Toughness ◽  
Bend Specimen

A novel impact bend test procedure is described/or determining the dynamic fracture-initiation toughness, KId, at a loading rate (stress intensity factor rate), K˙I, of the order of 106MPam/s. A special arrangement of the split Hopkins on pressure bar is adopted to measure accurately dynamic loads applied to a fatigue-precracked bend specimen. The dynamic stress intensity factor history for the bend specimen is evaluated by means of a dynamic finite element technique. The onset of crack initiation is detected using a strain gage attached on the side of the specimen near a crack tip. The value of KId is determined from the critical dynamic stress intensity factor at crack initiation. A series of dynamic fracture tests is carried out on a 7075-T6 aluminum alloy, a Ti-6246 alloy and an AISI 4340 steel. The KId values obtained for the three structural materials are compared with the corresponding values obtained under quasi-static loading conditions.

Thermal Stress Cleaving of Si-Wafer: Investigation of Fracture Initiation during Laser Beam Irradiation

2015 ◽  
Vol 1101 ◽  
pp. 412-418 ◽  
Author(s):  
Alias Mohd Saman ◽  
Tatsuaki Furumoto ◽  
Akira Hosokawa ◽  
Takashi Ueda
Keyword(s):  
Stress Intensity Factor ◽  
Thermal Stress ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Experimental Studies ◽  
Fracture Initiation ◽  
Laser Beam Irradiation ◽  
Color Pyrometer ◽  
Good Agreement ◽  
Si Wafer

This paper investigates the fracture initiation at the vicinity of a micro-groove caused by thermal stress through computational and experimental studies. Fracture initiation time has been determined by analyzing the stress intensity factor. Stress distribution was examined by using a finite element method, and the fracture toughness of the material was determined by using a Vickers indentation technique. The fracture initiation process was verified experimentally by monitoring the acoustic emission signals, while the temperature of the laser spot was also measured using two-color pyrometer. The result shows that stress intensity factor was increased with the increase in micro-groove sizes. Consequently, fracture initiation was attained faster. The simulation results show a good agreement with the experimental results in examining the fracture initiation and recognizing the ideal micro-groove parameters for laser cleaving process.

Parametric Equation of Stress Intensity Factor for Tubular K-joints under In-plane Bending Load

2005 ◽  
Vol 20 (2) ◽  
pp. 83-90 ◽  
Author(s):  
Y. B. Shao
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Surface Crack ◽  
Residual Life ◽  
Numerical Models ◽  
Accurate Estimation ◽  
Parametric Equation ◽  
Bending Load ◽  
Plane Bending

Stress intensity factor (SIF) is frequently used by designers to predict the integrity and residual life of a tubular joint containing a surface crack. In this study, a new numerical modelling method for cracked tubular K-joints has been presented. The proposed model has been verified from experimental results to be accurate and reliable in evaluation of the stress intensity factor for any tubular K-joint with a surface crack. Thereafter, parametric study for more than five thousand numerical models of tubular K-joints with a surface crack subjected to balanced in-plane bending load (IPB) has been carried out. A parametric equation to estimate the SIF value of any cracked tubular K-joint under IPB is then proposed based on the computed numerical results. Error analysis has been also carried out and it shows that the proposed equation can provide reliable and accurate estimation of the SIF value for cracked tubular K-joints under IPB.

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